A NEW APPROACH TO ENHANCE THE SENSITIVITY OF A HOT-WIRE ANEMOMETER AND STATIC RESPONSE ANALYSIS OF A VARIABLE-TEMPERATURE ANEMOMETER

A new hot-wire anemometer which has greater sensitivity than that of a conventional constant-temperature anemometer (CTA) was proposed. Sens itivity differences between a recently developed constant-voltage anem ometer (CVA) and a CTA provided a direct motivation of the present stu dy. To derive a factor which made the difference in sensitivity, stati c response analyses of a CTA and CVA were performed first by calculati ons and experiments. It was found that the major factor which is respo nsible for the sensitivity of an anemometer is not the working resista nce of a hot wire itself, but the change in the wire resistance with v elocity. Based on this analysis, a new anemometer circuit, Where the w ire working resistance increases with velocity - that is, the operatin g mode of the wire becomes variable-temperature - was proposed and nam ed a variable-temperature anemometer (VTA). The VTA was made by substi tuting a voltage-controlled variable resistor such as a photoconductiv e cell or a transistor for one arm of the bridge. By positively feedin g back the bridge-top signal to the input side of these electronic com ponents, the wire resistance could be increased with velocity automati cally. The enhanced sensitivity of the VTA was validated by comparing experiment with the CTA.